JOGL Transparency Problem

Hello,
I've been trying to make an application with OpenGL on Java under Eclipse, using JOGL.
I want to make a 3D head transparent in order to make the tongue and the oral cavity visible.
Even if I enable glColor and set the alpha value to 0.5f , the program seems to ignore that and consider all the alphas 1.
After digging a little bit more, I found out that, if I use ONE_MINUS_SRC_ALPHA for the destination the result I get is the same one as if I hadn't enabled blending at all. So, only depth test gets disabled, and the glEnable(GL2.GL_BLEND) statement is ignored. The objects are visible depending on the order they are drawn, even if I've chosen them to be 50% transparent. It's as if they are all opaque. The program ignores the glColorf4 statement I wrote.
If I use gl.glBlendFunc(GL2.GL_SRC_ALPHA,GL2.GL_ONE) I get the same result I would have got if I used gl.glBlendFunc(GL2.GL_ONE,GL2.GL_ONE) instead. So this shows me the program considers alpha is always equal to 1.